A micromachine is also called MEMS (Micro Electro Mechanical System), MST (Micro System Technology), and the like and refers to a comprehensive system combining a mechanical microstructure and an electric circuit. Unlike general semiconductor elements, the above-described microstructure has a three-dimensional structure and is partly movable in many cases. The micromachine can have various functions of a sensor, an actuator, an inductor, a motor, a passive element such as a variable capacitor, a switch, an optical element, and the like.
Note that the aforementioned electric circuit is generally formed using a semiconductor element and can control the operation of the microstructure, or receive and process a weak signal output from the microstructure.
Furthermore, micromachines can be classified according to their manufacturing methods. For example, there are bulk micromachines in which microstructures are manufactured using crystal anisotropy of a silicon substrate, and surface micromachines in which thin films are stacked over various substrates to manufacture three-dimensional microstructures (see Patent Document 1). In particular, the surface micromachines have attracted attention because a microstructure and an electric circuit can be formed over one substrate.
Furthermore, micromachines functioning as actuators can be classified according to their driving mechanism, e.g., into electrostatic, piezoelectric, electromagnetic, and thermal actuators. In particular, micromachines functioning as electrostatic actuators are easily fabricated and have high reliability because they can be manufactured by typical semiconductor processes.
Furthermore, electrostatic actuators can be classified into parallel-plate types, cantilever types, comb-drive types, rotational types, and the like. A display device using a DMD (Digital Micromirror Device) is known as an example of the parallel-plate electrostatic actuators. The display device using a DMD uses neither polarizers nor color filters, and therefore, has high light use efficiency. Hence, the display device using a DMD is said to be capable of displaying high-contrast, high-quality images.